Materia in New World is a resource that can be used to craft a desired named piece of gear from any expedition. There is a different materia for each expedition. It is not universal. This means you can not obtain materia from one expedition and use to craft an item from a different expedition.
This resource gives players an additional option to obtain specific gear if they are not having any luck obtaining the drop during their expedition runs.
Players can obtain Materia in two ways. You can obtain it by getting a named item from an expedition and salvaging that item. Any named expedition item can be salvaged into Materia of its corresponding expedition type (Garden of Genesis, Depths, Lazarus, etc.) This is useful if you are obtaining duplicate named items or a named item that you do not want. You can salvage it and turn it into a useful item.
You can also obtain materia by defeating the main boss of an expedition. This will yield you with materia of its corresponding expedition type.
Once you have obtained a certain amount of materia you can then use that materia to craft your desired expedition gear. You will need to make your way to the applicable crafting station. Then, simply find the “Unique Expedition Rewards” section and your desired item.
Each item will have a different materia cost. There are no other resources needed when crafting the expedition drop. All you need is the required amount of materia and you will be able to craft the item.